Laser diode (LD) pumped all-solid-state continuous wave (CW) single-frequency (SF) lasers have been very essential light sources for precision measurement, quantum optics and information, atom-based applications, laser radar, and so on, which benefit from their intrinsic merits of low noise, high stability, and good beam quality. Especially, a 1080 nm laser can realize type-II noncritical phase matching in a potassium titanyl phosphate (KTP) crystal, and, through a parametric down conversion process, the two-mode quadrature squeezed lights and a pair of Einstein–Podolsky–Rosen (EPR) entangled beams at 1080 nm can be directly generated just by pumping one nondegenerate optical parametric amplifier (NOPA) based on a type-II noncritical phase matched KTP crystal[3–5]. The scheme can be used for preparing the multi-partite continuous variable (CV) entangled states and establishing the complex quantum networks with a relatively simple implementation. In the scheme, the second-harmonic wave (SHW) 540 nm laser serves as the pump light field, and the fundamental wave 1080 nm laser provides the local oscillation light for homodyne detectors and injected signal light field of the NOPA, so the CW SF 1080/540 nm dual-wavelength laser acts with a significant role in the scientific researches of quantum information and quantum computation. For preparing the multi-partite CV entangled states and establishing the quantum networks, more NOPAs and homodyne detectors are required, and then a CW SF 1080/540 nm dual-wavelength laser with high output power is desired. However, the severe thermal effect and fierce mode competition of the high-power 1080/540 nm laser as well as its frequency drift with the temperature fluctuation and airflow of the ambient environment under long-term operation can induce the occurrence of multi-longitudinal-mode (MLM) oscillation and mode-hopping of the laser, which inevitably influence the stability of the quantum optical experiment systems. To prevent the instability of the experiment system, an SF dual-wavelength laser with broadband mode-hop-free tuning ability is desired, so that the laser can easily keep stable single-longitudinal-mode (SLM) oscillation under long-term operation. In the quantum optics experimental system, the continuously tunable SF 1080/540 nm laser can also be used to adapt to different KTP crystals with slightly different phase-matching wavelengths and match with an ultra-low expansion (ULE) Fabry–Perot (F-P) cavity to reduce the intensity noise and frequency drift of the laser. In addition, the tunable 1080 nm laser is also helpful for optical pumping of the atoms[8–11], where the continuous tunable SF 1080 nm laser is desirable for precisely matching its wavelength with the transition lines of the atoms, for example, the two-photon transition of cesium atoms (6S–7S)[10,11].
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